Ultraviolet emissions observed in the nuclear regions of Comets 1941 I (CUNNINGHAM) and 1937 II (WILK-PELTIER) appear to coincide with the absorption features of the late N-stars in the same spectral ... [more ▼]

Ultraviolet emissions observed in the nuclear regions of Comets 1941 I (CUNNINGHAM) and 1937 II (WILK-PELTIER) appear to coincide with the absorption features of the late N-stars in the same spectral region (λ 3 600-λ 3 850). This gives some evidence in favor of the assignment of the unidentified ultraviolet absorption bands of N-stars and of the unassigned cometary emissions to the same molecule, probably a polyatomic compound. Coincidences of a less striking nature are found between the MERRILL-SANFORD bands of N-stars and unidentified cometary emissions in the region λ 4 200-λ 5 200. [less ▲]

Seven spectrograms of Nova DQ Herculis obtained in May and October, 1950, reveal that the striking changes in the spectrum of the nebulosity observed between 1942 and 1949 continue, while the mean ... [more ▼]

Seven spectrograms of Nova DQ Herculis obtained in May and October, 1950, reveal that the striking changes in the spectrum of the nebulosity observed between 1942 and 1949 continue, while the mean velocity of expansion remains practically the same as in previous years. [less ▲]

New observational data on the spectra of thirteen planetary nebulae and their nuclei are given. New nuclei of the WOLF-RAYET type containing both nitrogen and carbon have been found. Previously adopted ... [more ▼]

New observational data on the spectra of thirteen planetary nebulae and their nuclei are given. New nuclei of the WOLF-RAYET type containing both nitrogen and carbon have been found. Previously adopted WOLF-RAYET designations have been modified. Nuclei of planetary nebulae, despite their occasional resemblance to WOLF-RAYET stars, should not be associated with the latter. [less ▲]

Solid hydrates of CH4, CO2, ... may be present in cometary nuclei and interstellar grains. The vapor pressures — hence the rates of sublimation — of the various hydrates are of the same order of magnitude ... [more ▼]

Solid hydrates of CH4, CO2, ... may be present in cometary nuclei and interstellar grains. The vapor pressures — hence the rates of sublimation — of the various hydrates are of the same order of magnitude while the vapor pressures of solid CH4, H2O, ... differ by very large factors. The relative abundances of the radicals which are observed in comets would be explained more satisfactorily by assuming the presence of solid hydrates. [less ▲]

The spectrum of Comet 1950b at heliocentric distance 2.65 A.U. shows a strong solar continuum concentrated in the nucleus and CN emission over a coma forty times larger. Comet 1951a at heliocentric ... [more ▼]

The spectrum of Comet 1950b at heliocentric distance 2.65 A.U. shows a strong solar continuum concentrated in the nucleus and CN emission over a coma forty times larger. Comet 1951a at heliocentric distance 0.91 A.U. is very unusual in showing a strong nuclear continuum and extremely weak CN emission over a coma only eight times larger than the nucleus. The former seems normal for a comet distance from the sun; the latter is probably a "fresh" comet, newly arrived near the sun from the swarm of cometary material postulated by Oort at the outer confines of the solar system. [less ▲]

Eight spectrograms of Comet 19481, covering the range of heliocentric distances from 0.65 to 2.21 A.U., have been obtained. Sodium emission is observed at r = 0.73 and r = 0.79 A.U. At large heliocentric ... [more ▼]

Eight spectrograms of Comet 19481, covering the range of heliocentric distances from 0.65 to 2.21 A.U., have been obtained. Sodium emission is observed at r = 0.73 and r = 0.79 A.U. At large heliocentric distances (r = 2.21) only CN and the λ 4050 group are observed. The CN bands show the usual complex structure due to the fluorescence excitation by solar radiation. The behavior of CH and that of CH2 are compared. Unidentified features are present within and between the Swan bands, as well as in the yellow-red region. [less ▲]

The spectra of seven Wolf-Rayet stars have been observed in the region λλ 6500-8800. For the identifications, tables of predicted lines of C II-IV, O II-IV, and Si III and IV were prepared. All strong ... [more ▼]

The spectra of seven Wolf-Rayet stars have been observed in the region λλ 6500-8800. For the identifications, tables of predicted lines of C II-IV, O II-IV, and Si III and IV were prepared. All strong emission lines are satisfactorily explained in the WC sequence; in the WN sequence, a fairly strong complex emission near λ 8240 remains unidentified. [less ▲]

An extensive program of observations, planned in advance, was carried out during the predicted return of Comet Bester in March and April, 1948, as the comet receded from heliocentric distance 0.8 A.U. to ... [more ▼]

An extensive program of observations, planned in advance, was carried out during the predicted return of Comet Bester in March and April, 1948, as the comet receded from heliocentric distance 0.8 A.U. to 1.55 A.U. The eighteen spectra obtained extend over various parts of the observable region from λ 3070 to λ 8760, most of them from λ 3500 to λ 6800 on grating dispersion. These, together with seventeen direct photographs, provide virtually a continuous record of changes in the comet during the observing period. Since the slit of the spectrograph was oriented along the tail, extending about 4.5 minutes of arc from the nucleus, our spectrograms record the extent of the various molecular bands away from the nucleus. Based on this material and on observations of other comets, the following topics are discussed: a) Variations with heliocentric distance, r.-In Comet Bester the ratios CN/C2, λ 4050/CH, λ 4050/CN, λ 4050/C2 and probably OH/NH all increase regularly with increasing r. No flares or sudden changes in spectrum were observed. b) Extent of bands from the nucleus.-CO+, N2+, λλ 3378, 3509, and 3674 are found exclusively in the tail; CN, C2, NH, OH, λ 4050, and NH2 follow in order of decreasing extent from the nucleus. c) The far ultraviolet region.-The ratio OH/NH varies from comet to comet, being somewhat less than unity for Comet Bester, greater than unity for Comet 1941d, and much less for 1947n and 1941c, which are in other respects comparable. In Comet Bester the OH bands have a peculiar rotational distribution, probably due to the fluorescence mechanism. d) The photographic regions.-Twenty lines in the "λ 4050 group" behave in Comet Bester as if they originate from one molecular species. e) The red and infrared regions.-The existence of bands (tentatively identified with the "red system" of CN) at λ 7906 is confirmed, and other bands of the "red system" at shorter wave lengths tentatively identified. A number of other faint maxima between λ 7000 and λ 8700 are noted. f) The spectrum of the tail.-Nine bands of the CO+ "comet-tail system" are recorded, the (3, 0) band being abnormally strong. Four bands of the "Baldet-Johnson system" of CO+ are observed. Tentative identifications of the "β system" of NO and the "Schumann-Runge system" of O2 are noted. The strong emissions at λλ 3378, 3509, and 3674 are identified with CO2+, the third ionized molecule to be identified in comet tails. A summary of identifications and conclusions is given at the end of the paper. [less ▲]